In modern optical communications networks it is common practice to implement a control plane (eg as defined in ITU-T recommendation G.8080) for network topology discovery and route computation. Typically, the control plane deploys various protocols that enable each node of the network to populate a respective topology database that may subsequently be used to compute end-to-end routes through the network. One such protocol is Open Shortest Path First (OSPF), although there are others. As is typical of network discovery and route computation protocols, OSPF defines various types of Link State Advertisement (LSA) messages, which may be flooded into the network by a node to convey network topology information to all of the other nodes in the network. Accordingly, a given node can use the information contained in received LSAs to populate and maintain its topology database.
OSPF and similar topology discovery and route computation protocols are commonly referred to as “in-skin”, because the topology discovery and route computation functionality is distributed across the nodes of the network, rather than being localized in one or more central servers.
A limitation of control-plane based protocols such as OSPF is that lower-cost network nodes often lack sufficient resources to store and process the volume of information that would be needed to enable extension of OSPF-like topology discovery and route computation functionality in the physical layer of the network. Furthermore, the volume of LSA-like messaging that would be needed to maintain an accurate view of the physical network would be burdensome for all but the most trivial of network topologies. Consequently, network operators typically utilize a centralized Path Computation Element (PCE) or server to compute end-to-end paths through the network physical layer.
However, as networks grow in size and complexity, the use of a centralized PCE may become disadvantageous. A known alternative is to divide the network into two or more sub-domains, each of which is associated with a respective PCE. However, this arrangement can increase complexity of network management, and does not address the problem that separate topology discovery and route computation functions are performed by different systems in different layers of the network. Many network service providers would prefer a single ‘in-skin” solution for all layers of the network.
Techniques that enable “in-skin” path computation through the physical layer of a communications network are therefore highly desirable.